Jet turbine engine fuel, including methanol and isopropanol



Patented Dec. 15, 1953 JET TURBINE ENGINE FUEL, INCLUDING METHANOL AND ISOPROPANOL Barrett B. Russell 3rd, Elizabeth, and Nathaniel H. Rickles, Roselle Park, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 22, 1948, Serial No. 66,826

4 Claims.

The present invention relates to an improved fuel for use in aviation gas turbine engines, jet propulsion engines, and similar types of power plants. In accordance with this invention, a fuel composition is provided having a high alcoholic content, whereby carbon deposition from combustion of the fuel is substantially minimized.

At the present time, the development of aviation power plants appears to point to a marked increase in the use of engines known as gas turbine engines and jet propulsion engines. It appears that in the future, many, if not most, airplanes will be powered by such engines. This development has placed a heavy burden on refineries insofar as supplying a suitable type of fuel, in sufiifciently large volumes for these engines. In view of the fact that present aviation fuels cannot be successfully used in such engines, it has been found that there are many problems involved in discovering and adapting suitable fuel compositions. Insofar as this invention relates to a fuel particularly adapted to meet three of the criteria of a successful jet fuel, these three criteria wil be discussed herein.

One of the outstanding requirements for a successful jet fuel is that it be comparatively clean burning. In the effectual operation of a jet turbine engine a combustion zone is positioned immediately in front of the blades of the turbine and consequently, any formation of deposits in the combustion zone creates the possibility that these deposits will pass from the combustion zone to impinge against the blades of the turbine. This possibility must beavoided since the turbine blades are precisely and delicately formed and since these blades are rotating at speeds of 16,000 E. P. M. or higher. Consequently, if deposits do form in the combustion zone and if these deposits are carried back to the turbine blades, the efficiency of the engine is greatly decreased and the effective life of the engine without overhaul is markedly lessened. This problem of deposit formation is particularly critical when fuels are used which result in the formation of carbon deposits in the combustion zone. The formation of carbon ordinarily occurs in a fairly adherent form on the lining of the combustion zone. However, after a period of carbon buildup, at frequent intervals a quantity of this carbon will strip from the liner or will chip oii causing fairly large size particles of carbon to impinge on the blades of the turbine. It is, therefore, one of the principal objects of this invention to provide a jet fuel which will substantially decrease the amount of carbon in the combustion zone.

A second critical characteristic of suitable jet fuels is the effect the combustion of the fuel has on the liner of the combustion zone. The jet turbine engine is ordinarily composed of an external cylinder within which is centrally positioned a liner; the combustion zone is inside this liner. The liner is positioned relative to the cylinder so that air passageways are provided around the liner within the walls of the cylinder. Openings are critically placedin the liner adapted to permit the proper inflow of air and fuel into the liner. In operating an engine of this type, it is clearly important to prevent warping or deformation of the liner since any warping that does occur will displace the air openings in a manner that will decrease the efiiciency of the combustion zone. It is known that combustion of certain types of fuels will tend to cause deformation of the liner. It is entirely possible that this deformation of the liner may be closely related to the problem of carbon deposit heretofore mentioned. Thus, localized deposition of carbon on the liner may cause localized cool spots effective to set up strains in the liner, resulting in the warping or deformation of the liner. It is therefore a further object of this invention to provide an improved fuel adapted to minimize this characteristic warping or deformation of the liner of a jet turbine engine.

One other specific object of this invention is to minimize the carburization of the metallic parts of the combustion zone and the associated parts of, the engine. It is known that ferrous metals and their alloys are readily susceptible to carburization in the presence of hydrocarbons at high temperatures. This is critical since the heat resisting qualities of structural metals appear to be related to their carburization qualities; alloys, which carburize readily fail more rapidly under operating conditions. The fuel of this invention is therefore intended to permit operation of jet engines with substantially less carburization of the metallic parts of the engine.

In accordance with this invention, it has been discovered that the above mentioned objectives may be attained by incorporating in a jet fuel, a fairly large proportion of an alcohol, or blends of alcohols. The base fuel to which the alcohol to be added may, if desired, be any type of fuel recognized to be suitable for use in a jet engine. For example, the base fuel may consist of the type of fuel designated or specified by Army and Navy jet fuel specifications such as AN-F-32. Essentially, thesefuels are narrow cut kerosene type fuels. They are particularly characterized as having particularly low cloud and freezing points and a boiling range such that the 10% distillation point is at a maximum of 410 F. and the final boiling point is at a maximum of 572 F. While it is particularly contemplated that the present inventive concept of employing alcohol in a jet fuel should be applied to fuel of this general character, the invention is not restricted thereto. Thus, it is contemplated that the pres ent invention will be of value in any fuel suitable for use in a jet engine whether or not that fuel meets the present Army-Navy fuel specifications.

In order to obtain the full benefits of this invention, it is preferred that approximately from 25% to 75% of alcohol be used in the fuel. It is contemplated that any alcohol having suitable solubility can be employed, although it is preferred that the alcohol be chosen from the class of -1 to C-3 alcohols consisting of methyl alcohol, vinyl alcohol, ethyl alcohol, allyl alcohol, normal propyl alcohol or isopropyl alcohol. It is apparent that the particular alcohol chosen and the particular amount of alcohol employed should be such that the resulting composition does not show cloud or freeze points within the limit set for a satisfactory jet fuel. While any one of the alcohols indicated may be employed, it is particularly proposed that mixtures of alcohols should be employed so as to permit the adjustment of the carbon to hydrogen ratio in the resulting fuel composition. Thus, for example, as it is desirable to obtain a jet fuel having a carbon to hydrogen ratio of about 6:1, it will be found desirable to employ a blend of methyl and iso-propyl alcohols so as to permit the convenient adjustment of the carbon to hydrogen ratio. 7

As stated, in practicing this invention, it is intended that from 25 to 75% by volume of alcohol be mixed with the base fuel stock employed. This fuel composition is then fed to the jet turbine engine in the conventional manner. It should be noted, however, that it is within the scope of this invention, if so desired, to separately inject the base fuel stock and the alcohol. While it is not presently thought desirable to employ a dual injection system for this purpose, it is contemplated that the objectives of this invention could be achieved by so doing.

The nature of this invention will be more clearly understood from a consideration of the following examples, showing adaptations of this invention. In these examples, a General Electric I-l6 combustor was employed. This combustor was set up in conjunction with compressed air supplies and fuel supplies to closely simulate operating conditions. Runs of five hour durations were made employing a variety of fuel compositions. For the sake of comparison, the runs were so conducted so as to maintain the outlet temperature of the combustor, which corresponds to the turbine inlet temperature of an actual plane, at an equal value for each run. To accomplish this, a constant air flow rate was maintained for all runs but the fuel flow rate was adjusted to secure the desired combustor outlet temperature. After the five hour run the cornbustor was carefully examined to determine the extent of liner distortion. A system of visual demerits was used wherein zero represented substantially no distortion and 100 represented the worst possible distortion. The quantity of carbon deposition in the liner was determined by carefully scraping the liner to enable actual weighing of the carbon deposits.

Example 1.-A catalytically cracked fuel stock.

propanol.

suitable fOr use in a jet turbine engine was employed. This fuel had the fuel composition and inspections indicated in Table I below.

Table I Gravity, API 33.7 Freezing point, "F 76 Flash point, F 123 Vol. percent aromatics 41 Carbon, weight percent 87.9 Hydrogen, weight percent 12.3 Sulfur, weight percent 0.024 Viscosity, K. V. at F 10.60 Diesel index 25 Heating value,B. t. u./gal 130,000 Distillation:

I. B. P 315 F. B. P 504 Carbon hydrogen ratio 7.15/1

The air flow rate employed was 1.92 lbs. per second. The fuel flow rate was 0037 lb. per second. The air to fuel ratio was 52 and the combustor outlet temperature was 1530 F. At the end of a five hour test run it was found that 44 grams of carbon had been deposited on the liner and the liner was given a fuel demerit indicative of its distortion, of 44.

Example 2.A similar test run was conducted employing a somewhat different type of jet turbine fuel. This fuel had the nature and inspections indicated in Table II below.

Table II A five hour test run was conducted employing the" conditions of operation given in Example 1 with the exception that the outlet temperature of the combustor was 10 higher. It was found that the amount of carbon deposited in the liner was 38 grams while the liner distortion as indicated by the fuel demerit assigned was 13.

Example 52-9. final run was conducted employing a fuel embodying the principles of this i invention. The fuel used was that employed in Example 1 having the characteristics shown in Table I. To the fuel of Example 1 was added by volume of a 50-50 blend of methanol and iso- This blend of alcohol was particularly chosen so that the carbon to hydrogen ratio of the fuel-alcohol blend was approximately 6.221. The fuel flow rate was adjusted so that the combustor outlet temperature was substantially the same as that in the first two examples. The actual combustor outlet temperature was 1525 F.

To achieve this, the fuel flow rate was selected as 0.043 lb. per second. The air flow rate was 1.92 lbs. per second to yield an air to fuel ratio of 44.5. It may be noted that if this fuel flow rate were corrected for the oxygen content of the alcohol the fuel fiow rate would be 0.039 lb. per second to give an air to fuel ratio of 49. After the five hour test run, it was found that the amount of carbon deposited on the liner was 13 gramn and that the fuel liner distortion demerit was 15.

It will be noted from the above three examples that by employing a jet fuel consisting of about by volume of alcohol, the amount of carbon deposited in the liner was substantially cut down. In the comparative fuels of Examples 1 and 3 the amount of carbon deposition was cut by approximately two thirds. Similarly, as shown by Example 3, the high alcoholic fuel of this invention resulted in markedly less liner distortion. Thus, in comparing Examples 1 and 3, the liner distortion resulting from the fuel of Example 3 was approximately one third that resulting from that used in Example 1.

Having now fully described this invention, What is claimed is:

1. A jet turbine fuel comprising" a hydrocarbon fuel base having an initial boiling point of about 315 a 10% distillation point below about 410 F., and a final distillation point below about 572 F., said fuel base having a kinematic viscosity at -40 F. of about 15.6, and about 25 to 75 percent by volume of a mixture of methanol and isopropanol.

2. The composition defined by claim 1 in which the said fuel base constitutes an aromatic base stock.

3. The composition defined by claim 1 in which the said fuel base constitutes a paraffinic base stock.

4. The composition defined by claim 1 in which the said mixture of methanol and isopropanol is selected to provide a carbon to hydrogen ratio in the fuel of about 6.2 to 1.

BARRETT B. RUSSELL 3RD. NATHANIEL H. RICKLES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 12,987 Gesner May 29, 1855 38,015 Tyler Mar. 24, 1863 1,361,153 Hayes Dec. 7, 1920 1,412,233 Ellis Apr. 11, 1922 2,446,523 Bradbury et al. Aug. 10, 1948 FOREIGN PATENTS Number Country Date 123,450 Great Britain Feb. 27, 19 9 437,484 Great Britain Oct. 25, 1935 OTHER REFERENCES Rockets, May-August 1946, page 7. Coast Artillery Journal, January-February 1948, pages 25-29. 

1. A JET TURBINE FUEL COMPRISING A HYDROCARBON FUEL BASE HAVING AN INITIAL BOILING POINT OF ABOUT 315* F., A 10% DISTILLATION POINT BELOW ABOUT 410* F., AND A FINAL DISTILLATION POINT BELOW ABOUT 572* F., SAID FUEL BASE HAVING A KINEMATRIC VISCOSITY AT -40* F. OF ABOUT 10.6, AND ABOUT 25 TO 75 PERCENT BY VOLUME OF A MIXTURE OF METHANOL AND ISOPROPANOL. 